Fluorination of boric acid and phosphorous acid

ABSTRACT

A method of producing boron trifluoride or phosphorus trifluoride using a metal fluorosulfonate fluoride, MF(FSO3), as the fluorinating agent is disclosed. Boric acid, H3BO3, and phosphorous acid, H3PO3, respectively, are employed as the boron or phosphorous source.

United States Patent 191 Wiesboeck 5] Apr. 17, 1973 [5 F LUORINATION OFBORIC ACID AND [56] References Cited PHOSPHOROUS ACID UNITED STATESPATENTS [75] Inventor: Robert A. Wiesboeck, Stone Moun- 1 min, Ga. v3,l58,658 l l/l964 Markowitz ..23/205 X [73] Assignee: i i SteeCorporation Primary Examiner-Oscar R. Vertiz l S mg AssistantExaminer-G. Alvaro [22] Filed: Sept. 27, 1971 Attorney-Gene Harsh et al.

21 A l.N 184,2 l 02 57 v ABSTRACT Related Apphcauon Data A method ofproducing boron trifluoride or [62] Division of Ser. No. 60,!47, July3i, 1970, Pat. No. phosphorus trifluoride using a metal fluorosulfonate3,635,673 fluoride, MF(FSO as the fluorinating agent is disclosed. Boricacid, H 30 and phosphorous acid, 52 us. Cl. ..423/301,423/4s3, 423/554Hams, respectively, are employed as the boron [51] Int. Cl. ..C0lb 25/10phosphorous Source [58] Field of Search ..23/205, 153

8 Claims, No Drawings FLUORINATION OF BORIC ACID AND PHOSPHOROUS ACIDThis application is a division of U.S. application, Ser. No. 60,147,filed July 31, 1970 now U.S. Pat. No. 3,635,673.

BACKGROUND OF THE INVENTION Conventional processes (USP 2,148,514 andUSP 2,196,907) for the production of boron trifluoride,

tion of boric acid, H 30 with fluorosulfonic acid,'

The preparation of phosphorus trifluoride, PF is based on the halogenexchange of phosphorus trichloride, PCI with hydrogen fluoride or withmetal fluorides such as zinc fluoride, ZnF, (T. Kruck, Angew. Chem.Intern. Ed. Engl. 6, 53 1967):

Pc1,+ 3HF PF3+ 3Hc'1 2PCl sznr 2I I= sznci SUMMARY OF THE INVENTION Thisinvention describes a novel method of producin g boron trifluoride andphosphorus trifluoride using a metal fluorosulfonate fluoride as thefluorinating agent and boric acid and phosphorous acid as the boron andphosphorus sources. The fluorination. also produces hydrogen fluoride asa reaction by-product which may be collected with the main product orseparated by fractional condensation.

The process is expressed by the following equation: H BO 3MF(FSO BF3llF-+ 3MSO H PO; 3MF(FSO PF 3HF 3MSO DETAILED DESCRIPTION Thefluorination of boric acid with an alkaline earth- 'fluorosulfonatefluoride, such as calcium or barium fluorosulfonate fluoride, iscarriedout by mixing the pulverized reactants thoroughly and heating to 50 350C, preferably 150 200 C, while excluding moisture.

An equimolar mixture of a metal fluoride and a metal fluorosulfonate,such as CaF and Ca(FSO,),, can be,

used in place of the fluorosulfonate fluoride, CaF(F- SO in this case,the cation may be chosen from any of the alkali or alkaline earthmetals. Any combination of salts of the alkali or alkaline earth metalchosen is effective as long as the molar ratio of fluoride tofluorosulfonate is approximately lzl.

The evolution of boron trifluoride in the fluorination of boric acidbegins at approximately 50 C, becoming quite vigorous at 150 200 C.Since the rate of reaction is dependent upon the particle size of thereactants, it is preferable that the particles should be smaller than 40mesh, and most preferable that they be 200 mesh.

The heating of the reactants can be carried out in an agitated vessel atatmospheric or super-atmospheric pressure. The gases may be vented ormay be allowed to accumulate in the reactor.

Of the many alkali or alkaline earth fluoride plus fluorosulfonatemixtures or alkaline earth fluorosulfonates which may be used to produceboron trifluoride and hydrogen fluoride from boric acid, I prefer toemploy calcium fluorosulfonate fluoride since it is the most economicalsource and maintains a dry, free-flowing reaction bed, resulting inhigher yields and easier handling.

Although the proportions of boric acid to the fluorosulfonate fluoridecan be varied widely, optimum utilization of the reactants is obtainedat a 1:3 molar ratio; i.e., one part by weight of boric acid to 7.6parts by weight of calcium fluorosulfonate fluoride.

The volatile reaction product consists of approximately equal portionsof boron trifluoride and hydrogen fluoride, which are either separatedby known methods or used together for certain catalytic applicationssuch as are disclosed in USP 3,458,590 and USP 3,441,538.

The fluorination of phosphorous acid follows closely that described forboric acid. Since phosphorous acid tends to decompose above 180 C,forming phosphine, it is advantageous to limit the reaction temperatureto C, and to inject the phosphorous acid as a melt (m.p. 73 C) into theagitated bed of hot calcium fluorosulfonate fluoride.

Calcium fluorosulfonate fluoride is the preferred fluorinating agentsince it produces highest yields and a dry, free-flowing reaction bed.The optimum utilization of reactants is achieved at a 1:3 molar ratio ofphosphorous acid to the fluorosulfonate fluoride; i.e., one part byweight of phosphorous acid to 5.8 parts by weight of calciumfluorosulfonate fluoride.

Purification and separation of the volatile reaction product may beachieved by any conventional means, as for example by passing the gasthrough a refrigerated column (-40 C) at atmospheric orsuper-atmospheric pressure, which condenses the hydrogen fluoride.Remaining traces of hydrogen fluoride may be removed from the phosphorustrifluoride by absorption on pelletized sodium fluoride at ambienttemperature.

The invention is further illustrated 'by the following examples:

Example 1 Calcium fluorosulfonate fluoride (48.2 g) and boric acid (6.2g) were mixed intimately in a mortar and placed in an aluminum reactorwhile excluding moisture by a blanketing atmosphere of dry nitrogen.After evacuation, the vessel was heated to 200 C over 2-hour period. Apressure of 240 psi developed. The gas was allowed to expand into anevacuated fractionation train with cold traps maintained at 78 and 1 96C, respectively. A total of 4.8 g of hydrogen fluoride and 5.2 g ofboron trifluoride was collected.

Example 2 An intimate mixture of sodium fluoride (12.8 g), sodiumfluorosulfonate (37.0 g), and boric acid (6.2 g)

Example 3 I Boric acid (12.4 g) and barium fluorosulfonate fluoride(154.2 g) was placed in a Teflon bottle and heated to 200 C over a3-hour period. The evolving gas was passed through cold traps maintainedat -78 and 196 C, respectively. After'completion of the reaction, a slowstream of dry nitrogen was passed through the reactor to-transfer theresidual gaseous product into the traps. The reaction produced 9.6 g ofhydrogen fluoride and 10.2 g of boron trifluoride.

Example 4 into a series of evacuated cold traps maintained at -78- and 196 C, respectively. A total of 4.5 g of hydrogen fluoride and 7.8 g ofphosphorus trifluoride was collected.

Example 5 Barium fluorosulfonate fluoride (255.0 g) g was placed in aTeflon bottle, equipped with a mechanical stirrer, and heated to 150 C.While stirring rapidly, a melt of phosphorous acid (27.0 g), maintainedat 100 C-was injected slowly. The evolved gas was passed Example 6 Amixture of calcium fluoride (39.1 g) and calcium fluorosulfonate (120.0g) was reacted with phosphorous acid(27.0 g) as described in Example 5.

After completion of the run, the cold traps contained 17.5 g of hydrogenfluoride and 26.9 g of phosphorus trifluoride, respectively.

Example 7 The process was carried out as described in Example 5 usingpotassium fluoride (58.1 g), potassium fluorosulfonate (138.9 g) andphosphorous acid (27.3 g). The product consisted of 15.0 g of hydrogenfluoride and 22.8 g of phosphorus trifluoride.

The above examples are intended to illustrate my invention and are notintended to limit it. I intend to cover all embodiments within thespirit of my disclosure. and intend to belimited only by the claimsappended thereto.

1 claim:

1.'The method of preparing phosphorus trifluoride comprising reactingmolten phosphorous acid with particles of an alkaline earthfluorosulfonate fluoride at a temperature of from about 73 to about C atatsmaller than size 40 mesh.

3. The method of claim 1 wherein the reaction products are separated byfractional condensation.

4. The method of claim 1 wherein the particles are 200 mesh.

5. The method of claim 1 wherein the alkaline earth fluorosulfonatefluoride is calcium fluorosulfonat fluoride or barium fluorosulfonatefluoride.

6. The method of claim 1 wherein the molar ratio of phosphorous acid tothe fluorosulfonate fluoride is about 1:3.

7. The method of preparing phosphorus trifluoride comprising mixingphosphorous acid with particles of an' alkaline earth fluorosulfonatefluoride and then heating the mixture to a temperature of from about 73to about 150 C at atmospheric pressure or above while excludingmoisture.

8. The method of claim 7 wherein said particles are smaller than size 40mesh.

2. The method of claim 1 wherein said particles are smaller than size 40mesh.
 3. The method of claim 1 wherein the reaction products areseparated by fractional condensation.
 4. The method of claim 1 whereinthe particles are -200 mesh.
 5. The method of claim 1 wherein thealkaline earth fluorosulfonate fluoride is calcium fluorosulfonatefluoride or barium fluorosulfonate fluoride.
 6. The method of claim 1wherein the molar ratio of phosphorous acid to the fluorosulfonatefluoride is about 1:3.
 7. The method of preparing phosphorus trifluoridecomprising mixing phosphorous acid with particles of an alkaline earthfluorosulfonate fluoride and then heating the mixture to a temperatureof from about 73* to about 150* C at atmospheric pressure or above whileexcluding moisture.
 8. The method of claim 7 wherein said particles aresmaller than size 40 mesh.